STORY ARCHIVE

Vesuvius

Naples is known for it’s great food and wine, and part of the reason for that is the rich volcanic soil in this region. But new research shows the very volcanism that’s brought Naples its great food bounty could also be its downfall. Some volcanologists believe Naples could become the next Pompeii – and quite possibly within the next year.

Graham Phillips visits Naples and Pompeii to understand why some experts think a major eruption is imminent and to see what a major eruption like the one that wiped out Pompeii in AD 79 would mean for Naples today..

TRANSCRIPT

Graham: Now Naples is known for its great food and wine, and part of the reason for that is the rich volcanic soil in this region. But new research shows the very volcanism that’s brought Naples its great food bounty could also be the city’s downfall. Some vulcanologists believe Naples could become the next Pompeii.

Narration: A clue to why they believe this city could one day be destroyed by a volcano, lies beneath the hustle and bustle.

Graham: I’m about forty metres under the city centre of Naples, in an old Roman aqueduct. They used to store water here. Now here’s the interesting thing. Look at the walls and they’re made out of volcanic outfall.

Narration: The Naples region has been covered before. The question is: could it be covered again?

If so it’d be disastrous. Three million people live here now, and quickly evacuating this already chaotic city would be a nightmare.

Mt. Vesuvius lies only a handful of kilometres from the outskirts of Naples. Vulcanologist Giuseppe Mastrolorenzo says recent research shows this volcano is a threat to the city. Giuseppe’s been studying and monitoring Vesuvius for years.

Professor Giuseppe Mastrolorenzo: Vesuvius has erupted several times during the last three hundred years. Hundreds of times.

The last period started in 1631 has been featured by a lot of relatively smaller eruptions.

Narration: These relatively small eruptions aren’t that small. The last one in 1944 destroyed several buildings in a nearby village.

But Naples hasn’t been threatened by any of these smaller eruptions. Which has given people a false sense of security, says Giuseppe.

The smaller eruptions are called strombolian, fed by only a small magma chamber. But much, much bigger eruptions are possible, when the magma from a larger chamber breaks through…an unnerving thought as I headed into the crater. The big ones have been dubbed Plinian.

Professor Mastrolorenzo: Plinian eruptions are featured by the production of a large amount of magma. The order of cubic kilometres of magma. All this material is erupted in a very short time, in the order of a few days, maybe one day, so this is why the Plinian eruptions are so violent.

Narration: The last Plinian was in 79AD, which devastated Pompeii. But again, Naples wasn’t destroyed. A view’s developed that this city is essentially safe from Vesuvius.

But new evidence is changing that. Researchers have found an earlier Plinian eruption.

Professor Roberto Scandone: It occurred during the bronze age and was an eruption the same size as the one that destroyed Pompeii and Herculaneum.

Narration: These remarkable footsteps in volcanic ash found near Naples were made by a bronze age person 2000 years before Pompeii.

Professor Mastrolorenzo: The most dangerous parts of the eruption travelled distances exceeding 25 kilometres even west and northwest of the volcano in the direction presently occupied by Naples.

Narration: Naples was covered that time. And to get a feel for what that would mean for Naples today if the same eruption occurred, you just have to visit Pompeii.

Graham: So this is a rich person’s house I’d say

Narration: Now why weren’t those frescos on the wall destroyed? The answer’s tied up with the different phases of a volcanic eruption.

First of all, a common misconception is that lava does the damage.

Professor Scandone: The liquid lava is not very dangerous unless it’s very fast. Usually during normal eruption the velocity of the lava flow is of the order of 10 metres maybe 100 metres per hour. So it’s very slow. You can stand in front of the lava flows.

Narration: The Pompeii residents didn’t suffer rivers of hot lava, rather…ash and pebbles of cool pumice raining down from the skies. This is Phase I of the eruption.

In the unexcavated sections of Pompeii the layer of pumice is clearly visible.

Professor Mastrolorenzo: This is the fallout deposit produced by the first phase of the eruption which lasted about twelve hours.

Graham: And how dense is it?

Professor Mastrolorenzo: This is a low-density material because it contains a lot of vesicles produced by the gas.

Graham: Yes, very light.

Narration: Pumice is solidified, frothy lava.

Professor Scandone: It’s thrown up into the sky and falls down like snow. So this forms a covering of all the landscapes.

Graham: So while that stuff is raining down. You could almost just go about your business. Have a good umbrella and you’d be right?

Professor Mastrolorenzo: Mostly yes, but in some cases there are larger blocks like these, which are lava blocks.

Narration: The raining debris broke house rooves, but it filled the houses…protecting those frescos.

Graham: So that initial pumice that came down. Filled this up to here.

Professor Mastrolorenzo: So everything was protected. So just the very upper parts were destroyed.

Narration: In Naples much the same thing would happen. And the 12 hours of pumice rain would be the window of opportunity for Neapolitans to escape. Because afterwards the devastating Phase II of the eruption begins.

The world watched a Phase II eruption a few decades ago. Mt. Piniatubo.

Professor Scandone: The last Plinian eruption occurred in the Philipines: the eruption of Pinatubo in 1991 which was similar to the one that destroyed Pompeii and Hercleon.

Narration: A mixture of ash and larger pieces, called tephra, was blasted 35 kilometres up in a column. And because it’s hot, it has a low density, and therefore rises.

But as it cools, it becomes more dense, and eventually heavier than the surrounding air. Gravity wins and the column collapses.

Professor Mike Sheridan: It starts slipping down the sides and cascading down to the ground like a waterfall in all directions, and then it moves out by gravity where the topography directs the movement of these flows.

Narration: Mike Sheridan from the University at Buffalo has made mathematical models of the deadly column collapse.

These are called pyroclastic flows.

Professor Scandone: The pyroclastic flow is the most dangerous part of the eruption because it flows along the ground and it has very high temperature. It may reach a temperature of 900 degrees Celsius and it usually destroys everything it encounters along its path.

Narration: It can move at 100s of kilometres an hour packs a punch 10 times a class 5 hurricane and is impossible to escape.

The denser rock layer above the pumice is the pyroclastic flow. It destroyed everything including any people who hadn’t evacuated.

Professor Scandone: So part of the people remained closed in the house, repairing from the fall of the pumice. And so they were trapped in the houses. If you go to Pompeii you find a large group of people who died in the eruption but you find these people above the pumice. You find above the pumice at the minute the pyroclastic flow arrived.

Narration: But why did Naples escape the Pompeii eruption and not the earlier Avelino one? The reason is the shape of the landscape directs the pyroclastic flow.

Professor Sheridan: During the time of the Avilino the landscape was sloping towards Naples. Whereas in the case of the Pompeii eruption, there was an opening more to the south and not in the direction of Naples

Narration: It begs the question: which way is the opening today?

Graham: When the next big eruption occurs a column of material will be ejected out of there 35 kilometres into the sky. Now when that collapses it will go in all directions but the current shape of the volcano suggests it will preferentially headed towards Naples.

Narration: The mathematical models predict the path.

Professor Sheridan: So if these flows are moving on land they would be potentially directed toward the northern part of the city of Naples. If they could travel across the Gulf of Naples, across the water they could go directly across.

Narration: The good news is, there should be some warning. Vesuvius is the most heavily monitored volcano in the world.

Professor Sheridan: There would be features like gas emissions from the volcano. There would be many earthquakes as this molten material moves into the ground under the volcano. And there would be ground deformation. The volcano would start swelling up like a woman before birth swells up.

Narration: The trouble is, predicting when that will happen is impossible.

Professor Mastrolorenzo: Unfortunately we could have a Plinian eruption even next year.

Narration: Or it may not happen for 100s of years or even longer.

But Giuseppe believes the possibility must be taken into account and an appropriate evacuation plan developed for Naples.